Calculating Insulin Dose

You'll need to calculate some of your insulin doses.

You'll also need to know some basic things about insulin. For example, 40-50% of the total daily insulin dose is to replace insulin overnight.

Your provider will prescribe an insulin dose regimen for you; however, you still need to calculate some of your insulin doses. Your insulin dose regimen provides formulas that allow you to calculate how much bolus insulin to take at meals and snacks, or to correct high blood sugars.

First, some basic things to know about insulin:

Approximately 40-50% of the total daily insulin dose is to replace insulin overnight, when you are fasting and between meals. This is called background or basal insulin replacement. The basal or background insulin dose usually is constant from day to day.

The other 50-60% of the total daily insulin dose is for carbohydrate coverage (food) and high blood sugar correction. This is called the bolus insulin replacement.

Bolus – Carbohydrate coverage

The bolus dose for food coverage is prescribed as an insulin to carbohydrate ratio.The insulin to carbohydrate ratio represents how many grams of carbohydrate are covered or disposed of by 1 unit of insulin.

Generally, one unit of rapid-acting insulin will dispose of 12-15 grams of carbohydrate. This range can vary from 6-30 grams or more of carbohydrate depending on an individual’s sensitivity to insulin. Insulin sensitivity can vary according to the time of day, from person to person, and is affected by physical activity and stress.

The bolus dose for high blood sugar correction is defined as how much one unit of rapid-acting insulin will drop the blood sugar.

Generally, to correct a high blood sugar, one unit of insulin is needed to drop the blood glucose by 50 mg/dl. This drop in blood sugar can range from 30-100 mg/dl or more, depending on individual insulin sensitivities, and other circumstances.

Examples:

Read some examples and therapeutic principles on how to calculate the carbohydrate coverage dose, high blood sugar correction dose and the total mealtime insulin dose.

Example #1: Carbohydrate coverage at a meal

First, you have to calculate the carbohydrate coverage insulin dose using this formula:

CHO insulin dose = Total grams of CHO in the meal ÷ grams of CHO disposed by 1 unit of insulin (the grams of CHO disposed of by 1 unit of insulin is the bottom number or denominator of the Insulin:CHO ratio).

This example illustrates a method for calculating of your background/basal and bolus doses and estimated daily insulin dose when you need full insulin replacement. Bear in mind, this may be too much insulin if you are newly diagnosed or still making a lot of insulin on your own. And it may be too little if you are very resistant to the action of insulin. Talk to your provider about the best insulin dose for you as this is a general formula and may not meet your individual needs.

The initial calculation of the basal/background and bolus doses requires estimating your total daily insulin dose:

Basal/Background and Bolus Insulin Doses

Basal/background insulin dose:

Basal/background Insulin Dose = 40-50% of Total Daily Insulin Dose

Example:

Assume you weigh 160 pounds

Your total daily insulin dose (TDI) = 160 ÷ 4 = 40 units.

In this example:

Basal/background insulin dose =50% of TDI (40 units) = 20 units of either long acting insulin, (such as glargine or detemir) or rapid acting insulin if you are using an insulin pump (continuous subcutaneous insulin infusion device).

This example above assumes that you have a constant response to insulin throughout the day. In reality, individual insulin sensitivity varies. Someone who is resistant in the morning, but sensitive at mid-day, will need to adjust the insulin-to-carbohydrate ratio at different meal times. In such a case, the background insulin dose would still be approximately 20 units; however, the breakfast insulin-to-carbohydrate ratio might be breakfast 1:8 grams, lunch 1:15 grams and dinner 1:12 grams.

While the calculation is 1 unit will drop the blood sugar 45 mg/dl, to make it easier most people will round up or round down the number so the suggested correction factor may be 1 unit of rapid acting insulin will drop the blood sugar 40-50 mg/dl.

Please keep in mind, the estimated insulin regimen is an initial “best guess” and the dose may need to be modified to keep your blood sugar on target.

Also, there are many variations of insulin therapy. You will need to work out your specific insulin requirements and dose regimen with your medical provider and diabetes team.

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